Magneto-inductive, flow measuring devices utilize the principle of electrodynamic induction for volumetric flow measurement and are described in a large number of publications. Charge carriers of the medium moved perpendicularly to a magnetic field induce a measurement voltage in measuring electrodes arranged essentially perpendicular to the flow direction of the medium and perpendicular to the direction of the magnetic field. The measurement voltage induced in the measuring electrodes is proportional to the flow velocity of the medium averaged over the cross section of the measuring tube and, thus, proportional to the volume flow rate. If the density of the medium is known, the mass flow in the pipeline, respectively in the measuring tube, can also be determined. The measurement voltage is usually sensed via a measuring electrode pair, which, relative to the coordinate along the measuring tube axis, is arranged in the region of maximum magnetic field strength and where, thus, the maximum measurement voltage is to be expected.
WO 2004/072590 A1 discloses a magneto-inductive, flow measuring device having two coil bodies arranged oppositely on a measuring tube and having, in each case, a coil and a pole shoe as coil core. The pole shoe is held in a first passageway of the coil body along the coil axis. It includes a broadened part, which is so embodied that the measuring tube is contactable by the pole shoe approximately gap-freely. The coil bodies are mutually biased by means of two field guide-back elements. In this way, the respective pole shoes are pressed against the measuring tube.